1. Field of the Invention
This invention generally relates to sound transducers. More particularly, the present invention relates to substantially planar sound transducers also known as flat loud speakers.
2. Description of the Prior Art
Prior art flat loud speakers typically include a diaphragm that is constructed from a substantially planar panel of molded styrofoam or other suitable material. The diaphragm is usually suspended from a support frame by a layer of foam rubber or the like. The front side of the diaphragm is generally smooth while the back side or frame side of the diaphragm has various shapes and channels molded therein so as to divide the panel into a plurality of regions, each region being suited for reproduction of sound in a particular frequency range. A plurality of cross members are attached to the support frame and at least one electromagnetic driver is attached thereto so that its electromagnetic coil is situated above a corresponding hammer that is attached to a predetermined region on the back side of the diaphragm.
Typical prior art flat loud speakers, methods of manufacturing the same, and components thereof are disclosed in the following prior U.S. Pat. Nos. issued to the herein inventor: 4,257,325; 4,184,563; 4,003,449; 3,801,943; 3,792,394; 3,779,336; 3,767,005; 3,722,617; and 3,596,733. The foregoing patents are hereby incorporated by reference as if fully set forth herein.
In ordinary speaker systems, it is generally necessary to have at least one electromagnetic driver and conical diaphragm that are suited for low frequency signals and a separate electromagnetic driver and diaphragm that are suited for high frequency signals. Frequently, a driver and diaphragm that operate best in the midrange are also employed.
In ordinary paper cone sound systems that typically use paper cone-shaped diaphragms, a diaphragm used for producing low frequencies is not physically coupled with a diaphragm used for producing high frequencies. There is little concern with respect to interference or intermodulation between the low frequency vibrations and the high frequency vibrations where separate diaphragms are uses so that there is no physical coupling between the diaphragms.
Flat planar speakers were developed in part to closely approximate reality by reproducing all frequencies in the sound spectrum from a single source diaphragm. However, because a flat loud speaker is constructed from a substantially planar diaphragm having at least one unitary smooth surface, the various regions of the diaphragm are physically coupled to one another by the common surface of the diaphragm.
One problem that has been experienced with the prior art flat loud speakers is interference or intermodulation between the low frequency and high frequency regions of the speaker.
Because of the physical coupling of the various sound reproduction regions by the common surface, it becomes necessary to isolate and limit the low frequency sound reproduction regions of the diaphragm so that the large low frequency vibrations do not unduly interfere or intermodulate with the high frequency sound reproduction regions. However, while desirable to isolate the low frequencies from the high frequency regions, it is still desirable to avoid directivity and increase the omnidirectional production of high frequency by allowing the high frequencies to emanate from the overall surface of the flat speaker system.
In the prior art flat loud speakers, limited isolation or dampening was partially accomplished by surrounding the high and low frequency sound reproduction regions with endless grooves that extend inward from the back side of the diaphragm. While such isolation grooves help solve the interference problem, the high frequency sound reproduction regions still continue to experience detrimental interference from low frequency vibrations that are transmitted through the common planar surface of the diaphragm.
Another problem that has been experienced with prior art flat loud speakers relates to the limited range of frequency reproduction that results from the economic desirability of selecting a unitary diaphragm material that represents a less than ideal compromise between high and low frequency reproduction.